There's actually a surprising number of animals that are naturally known to be cannibalistic anyways, and they range from insects, aquatics, rodents, to higher mammals like primates.
@Harvester The irony of your name aside for making a comment like this, it's true. I'm mostly an insect fan, and a lot of them tend to eat either their own species (some spiders will even prey on their own babies if they go hungry) and let's not even get into aphids (like wasps and hornets) who hunt bees. =/